You have to have a Fly Fishing Rod and some Feathers to fly fishing.
You also need an appropriate fishing level, and you need to go to a place for fly fishing, for example, the river near the Barbarian Village.
you cant fly a eagle in runescape the only game i know with eagles and flying is world of warcraft.
from 1-20 just fish the best thing you can do, then at 20 fishing fly fish at barbarian village till 99 :L
You can temporarily fly with Quest Emote or Puppet Master.
The best way to fish on runescape is to use a net or a fishing rod and bait in draynor. Then it is easy to bank your fish
A fly fishing rod
On the pier in Karamaja ;)
Raw fish.
From Runescape Wikia: "The Cavefish are a type of fish that can only be found in the Living Rock Caverns. The Living Rock Caverns can be found underneath the Dwarven Mine..."
There are various spots throughout all of runescape you can harpoon fish, the main ones are catherby, the fishing guild, and the island of karajama
Bass is a members only fish, only members can fish it.